Well-designed analogs of the naturally occurring ribo- and deoxyribonucleotides that are conformationally restricted by a transglycosidic tether would be valuable as biochemical, pharmacological, and biomedical probes and would have wide use in such fields of study as endonucleases, topoisomerases, ribozymes, oligonucleotide interstrand recognition, and many types of DNA and RNA structure-function relationships. However, the elements of their design must meet stringent criteria: (1) minimal structural disturbance caused by presence of the tether, (2) preservation of every natural hydrogen- bond donating/accepting molecular recognition site, (3) accessibility to both pyrimidine-and purine-based analogs, (4) conformational restriction of the glycosidic bond in the most commonly found bioactive anti form to retain the potential of A.T and C.G Watson-Crick-style base-pairing interactions, and (5) retention of all carbohydrate oxygen functionalities to allow potential incorporation into DNA or RNA oligonucleotide strands. The work will involve design, synthesis, and characterization of two new classes of nucleotide analogs that meet all of these criteria: (Class I) transglycosidically tethered ribo- and 2'-deoxyribonucleotide analogs derivable from 6-substituted pyrimidine and 8-substituted purine nucleosides and (Class II) transglycosidically tethered 2'- deoxyribonucleotide mimics derivable from 6-substituted pyrimidine and 8-substituted purine arabinofuranosides. The primary goal will be synthesis of the target Class I and II nucleotides in sufficient quantity for full structural characterization and for in-house and collaborative enzymatic, structural, and biological assays. Aspects of connectivity, stereoisomerism, and conformation in solution will be determined using high-field NMR spectroscopy; those in the solid state will be established by X-ray crystallography. Di-and triphosphates will be prepared, as will dinucleotides and related phosphoramidites. The Class I design will be modified to include structural features that may precipitate the irreversible inactivation of certain phosphodiester bond-hydrolyzing enzymes. Molecular modeling will be used to compare targets with natural counterparts, to analyze oligomers that will contain targets, and to evaluate potential interactions with enzymes of biomedical importance. All promising materials will be evaluated for antitumor, antiviral and biocidal potential.